This invention relates generally to systems for testing the conditions of lead-acid batteries, as well as starters and alternators used in conjunction with the batteries. In particular, the present invention relates to such testers that are microprocessor-controlled hand-held units.
The following symbols will have the following meanings in the description of the preferred battery testing system embodying this invention:
V(bat) The terminal voltage of the battery.
V(d) Voltage drop across the battery due to an internal resistance and a load current.
CA Cranking Amps, the current that the battery can supply for 30 seconds at full charge and at 70xc2x0 F. and not drop the battery voltage below 1.2 volts per cell.
Cold Cranking Amps (CCA) are defined by the Battery Council International (BCI) as xe2x80x9cthe number of amperes a battery at 0xc2x0 F. (xe2x88x9217.8xc2x0 C.) can deliver for 30 seconds and maintain, at least, a voltage of 1.2 volts per cell (lead-acid)xe2x80x9d. For example, a 12-volt lead-acid battery having 6 cells with 1.2 volts/cell must not drop below 7.2 volts. A fully charged battery has an open circuit voltage of 12.6 volts. The voltage drop from 12.6 volts to 7.2 volts is 5.4 volts. Therefore, at 0xc2x0 F., the CCA of the battery is the current that the battery can supply and drop the voltage not more that 5.4 volts at the end of 30 seconds. For a 6-volt lead-acid battery, the maximum drop is 2.7 volts and for a 24-volt lead-acid battery, the maximum drop is 10.8 volts.
It is an object of the invention to provide an improved hand-held testing unit that uses a microprocessor to perform test measurements on lead-acid batteries and the systems in which they are used, including the starters and alternators in such systems.
A specific object of one preferred embodiment of the invention is to provide such a hand-held testing system which is light and portable and yet is capable of subjecting lead-acid batteries to a load test drawing current as high as 200 amperes from the battery.
Still another object of the invention is to provide a hand-held battery testing system that is capable of subjecting a lead-acid battery to a load test without significantly reducing the state-of-charge of the battery.
Another object of the invention is to provide such a hand-held testing system that permits the user to load test a lead-acid battery, check the condition of the alternator, and perform a starter draw test with ease, using a single test unit.
Still another object of the invention is to provide such a testing unit that permits the test results to be printed and/or downloaded to a computer.
Yet another object of the invention is to provide a hand-held testing system that can also be used as a voltmeter.
In this connection, a related object of the invention is to provide such a system that automatically checks whether the tester is properly connected to the battery before the battery is subjected to the load test.
In accordance with the present invention, the foregoing objectives are realized by providing a system that determines the condition of a lead-acid battery by measuring the beginning voltage across the terminals of the battery in the absence of a load; connecting the battery to a first load, measuring the AC ripple in the output current drawn from the battery by the first load, and computing an estimated CCA of the battery using the beginning voltage and the AC ripple; connecting the battery to a second load that draws more current from the battery than the first load and measuring the loaded voltage of the battery, and evaluating the condition of the battery at least in part on the basis of the beginning voltage and the estimated CCA.